Around 1,200 Olympic workers had to be quarantined in their rooms earlier this week as they waited for norovirus test results to come back. No athletes have been reported sick yet, but police officers, Olympic security personnel, and food preparers have all fallen ill. Officials have brought in at least 900 military personnel to replace some of the sick security workers, whose symptoms included diarrhea and vomiting.

Symptoms surface between 12 hours and two days after exposure, and stem from inflammation in the stomach and intestines. In addition to diarrhea, patients can experience stomach pain, fever, body aches and vomiting.

Most people can recover from a norovirus episode in a few days without treatment by drinking plenty of fluids. But babies and the elderly, as well as people with compromised immune systems, can suffer severe hydration and need medical attention. According to US CDC, thousands of Americans wind up in the hospital with norovirus every year, and hundreds die.

Sasha Rearick, head coach of the US men's ski team told USA Today that the team has its own compound with separate chefs, and athletes wash their hands a lot.

How you get norovirus

The virus sheds from the feces of infected people and animals. You can get norovirus from eating contaminated food, drinking contaminated water, or putting hands contaminated with the virus (usually found in feces or vomit) in your mouth. Norovirus is a pretty hearty virus: it shows up in stool samples before people start feeling sick, and can stay in feces for two weeks after you feel better, according to the CDC. It sticks around on surfaces, too, so you don't have to come in contact with someone else's skin to get it.

Norovirus thrives in both hot and cold temperatures, and it's not easy to wipe away with disinfectant either, the Mayo Clinic says. Most people are still contagious up to two days after they start feeling better.

The stomach flu can also commonly break out in closed environments like cruise ships, nursing homes, and daycares. But there are recent reports of the illness circulating at athletic events, too. Last year at the world athletics championships in London, the virus quickly spread through one hotel, and several athletes had to withdraw from the first days of the tournament, The Guardian reported.

According to the CDC, norovirus causes 19 to 21 million illnesses in the US every year. Between 56,000 and 71,000 people have to be rushed to the hospital annually, and 570-800 die. The illness is responsible for one in every five diarrhea cases worldwide.